A turbine generally comprises several successive casings along the longitudinal axis of the turbine, such casings provide protection to the turbine elements or form flow paths or veins wherein air flows through the turbine.
Such casings are generally annular, extend along the longitudinal axis of the turbine, and have to be perfectly aligned so as to limit disturbances in the air flow, more particularly when the casings form flow paths or veins.
The casings each comprise an annular flange through which they are assembled together by bolting.
In a junction area of the downstream end of the combustion chamber casing with a turbine casing, as schematically illustrated in FIG. 1 which shows a turbomachine 4 turbine 2 of the prior art, the turbomachine comprises a fan disc 6 sucking air towards a downstream low pressure compressor 8, followed by a high pressure compressor 10 which opens into a combustion chamber 12. The combustion chamber 12 opens into a high pressure turbine externally delimited by a high pressure turbine casing 14 followed by a low pressure turbine externally delimited by a low pressure turbine casing 16. The high pressure and low pressure turbine casings 14, 16 are separated by at least one intermediate casing 18 specifically used for fixing the supports 20 of the shaft bearings 22, 24 of the different turbines. Both ends of the intermediate casing 18 comprise a flange 26, 28 radially extending outwards, and whereon the high pressure turbine casing 14 and the low pressure turbine casing 16 are attached.
Besides, a support 30 of the turbine is also attached to one of the two flanges 26, 28.
Such attachment however has a major drawback. An axial and radial shifting of the attachment between the high pressure turbine casing and the intermediate casing will affect the relative position, and thus the coaxiality, of the high pressure turbine casing with the low pressure turbine casing.
Moreover, the positioning of the upstream flange of the low pressure turbine casing has to be very accurate since such flange of the low pressure turbine casing is positioned in a zone where the clearance control ducts are integrated.
An axial misalignment of the casings can then create disturbances in the circulation of the air flow, impacting the efficiency of the turbine, and thus, that of the turbomachine.
Besides, such misalignment can be increased by the deformation, caused by heat, of the casings when the turbine is operating.
A solution would be to eliminate the intermediate casing to attach both turbine casings together, however the presence of such intermediate casing is necessary, specifically to enable attaching the turbine to the aircraft.